In a variety of forms warmth is relaxing and pleasurable to most people--basking in the sun; sitting by an open fire or a woodstove; reclining in a hot bath, whirlpool or spa; dressing in a warm room; a warm, dry towel after a shower or bath--all of these experiences are enjoyable. Many of them require some form of heating device, and heating devices of many types are widely available to fulfill the requirements. In some cases, however, the available heating devices have significant disadvantages.
For example, the water for bathtubs, spas, hot tubs, whirlpools and the like is almost always heated by a water heater. In most installations the water in those vessels cannot be recirculated through the water heater, so the only way to maintain or increase the water temperature is to add more hot water, perhaps releasing some of the cooled water to make room for the added hot water. For another example, keeping an entire apartment or house warm in cold weather is expensive. Therefore, it is desirable from an economic point of view to use a space heater, preferably on a periodic basis, to warm up a room, commonly a bathroom, for dressing. Many of the available types of space heaters can be dangerous if not used with care. The main hazard is fire, which can result from a towel or clothing dropping onto the heater or placing the heater too close to a flammable object.
An example of an extremely costly and wasteful use of heat for comfort and pleasure is a heated swimming pool or hot tub. The installation for heating swimming pools and hot tubs costs several thousands of dollars, and many hundreds of dollars have to be spent for fuel each year.
It is known, per se, to maintain or increase the temperature of the water in a bathtub and at the same time provide a whirlpool effect by bubbling heated air into the water. Examples of devices for this purpose are found in U.S. Pat. Nos. 1,350,974 (Kolshorn, Aug. 24, 1920); 3,065,746 (Gregory, Nov. 27, 1962); 3,075,520 (Sparks, Jan. 29, 1963); 3,111,686 (Sierant, Nov. 26, 1963); 3,138,153 (Osborn et al., June 23, 1964); 4,040,415 (Kulisch, Aug. 9, 1977); 4,245,625 (Murray, Jan. 20, 1981); and 4,535,490 (Wright, Aug. 20, 1985). To the extent that those patents describe specific heating devices, all of them use electrical heating elements that are in direct heat transfer contact with the air flow that is delivered by them. None of the devices of those patents provides protection against fire due to overheating of the heating element.
Safety against an electrical shock of any electrical appliance used near water is of paramount concern. The prior art tub-heating devices appear by and large to have ignored the shock hazard, which can result from water backing up in the air supply pipe into the heating unit or from accidental immersion of the unit. An exception is the tub massage apparatus described and shown in U.S. Pat. No. 4,040,415 (Kulisch, Aug. 9, 1977), in which a blower/heater unit operating on no more than 24 volts is powered by line current through a power pack (transformer) located remotely from the tub. The patents referred to above disclose a variety of forms of devices for injecting air bubbles into the tub, the most common one being a tube positioned around the perimeter of the tub bottom. Perimeter tubes are cumbersome to install, remove and store and release the air bubbles primarily at the sides of the person's body, not under the body. Another form is a pad or mat of the type shown in U.S. Pat. No. 4,417,568 (Nozawa et al., Nov. 29, 1983), which has the advantage of being foldable but the disadvantage of being hard and, therefore, uncomfortable. U.S. Pat. No. 4,008,498 (referred to above) proposes a water-filled compartmented mat (like a water bed) with air tubes extending lengthwise along it.
In temperate climates, such as most of the continental United States, there are times of the year when swimming pools are not environmentally heated enough to be usable, but days pleasant enough to make use of a swimming pool are abundant. As far as the present inventors are aware, there are no devices available for making swimming pools comfortably useful other than costly pool water heaters.